Thursday, February 18, 2010

“When Will They Hatch?”

Now that the eagles are settled in and incubating their three eggs - the big question is when will the eggs hatch? In addition to our knowledge about bald eagle biology, we have this pair's previous history to help guide us.

The scientific literature generally reports an incubation period of 35 days (although various authorities may list 34-38 days). Directly observing when bald eagles lay eggs and when they hatch has always been a challenge for biologists, sometimes limiting how precisely we could record events. The advent of technology such as the Eagle Cam has allowed both researchers and the public an unprecedented view of what actually happens in the nest.

We can now document when eggs have been laid and when they hatch with great accuracy (often to the minute). This will help us to better understand the nesting ecology of these birds. A table of the egg laying and hatch dates since the camera has been active is included below. Given past history - the average time for this pairs first egg to hatch has been just over 38 days (38days 3.6 hours). This would put our first egg hatching on March 9th. The second egg has hatched after an average of 37 days 7 hours and the third has averaged 36 days 3 hours. There is a clear trend of reduced incubation times for later eggs. By ensuring that the eggs hatch closer together, the disadvantage of the youngest chick is minimized. The eagles accomplish this by delaying full time incubation of the first egg (and to a lesser degree the second). This slows development and helps reduce the difference in hatch dates. It will be interesting to see if the trend holds true this year. As the first egg was laid in a snowstorm -the adults had to begin incubating it immediately. Whether or not this will have any effect in hatch dates remains to be seen.

Saturday, February 06, 2010

“Egg Number 3!”

Just as the rain and sleet of another Northeaster began to turn to snow - a third egg was laid by the bald eagles at the Norfolk Botanical Garden. Just after 12:29 pm the female laid what should be the final egg of this clutch. The video below shows some of her labor and a brief view of the eggs at 12:29:50 of the camera's time stamp.

The female is currently resting and keeping all three of her eggs warm and dry.

Sunday, January 31, 2010

“1st Egg”

The first egg was laid in a snowy nest at about 2:15pm on Sunday January 31st. Eagles (and many other birds) will often delay incubation until all of the eggs are laid. This helps ensure that the young hatch more closely together - keeping the youngest hatchlings from being too disadvantaged.

Even in relatively cool weather the eggs remain viable for some time without incubation...a nest full if snow is another matter altogether. To keep the egg from being excessively chilled the female has begun incubation (see picture below). Hopefully the female's body heat will melt away the snow and keep the egg at an optimal temperature (105 degrees). The snowy weather represents a challenge that this pair doesn't often have to deal with but that bald eagles as a species are well adapted for. Some have asked if the female would wait until better weather conditions to lay her first egg - unfortunately once the procees has begun and an egg has entered the female's oviduct there is no stopping it.